The present invention relates to the field of centralizers used downhole in wells. More particularly, the invention relates to an integral joint centralizer for incrementally increasing the radial force exerted by a movable centralizer element.
Conventional centralizers provide standoff in a wellbore or casing string to centralize tubulars or tools or to facilitate even distribution of cement around the tubular. Numerous centralizers have been developed to provide different functions downhole in a well.
One type of centralizer is a solid body centralizer. One example of a conventional solid body centralizer is illustrated in U.S. Pat. No. 5,881,810 to Reinholdt et al. (1999). Solid body centralizers provide standoff and cement distribution properties but can be difficult to install in lengthy horizontal and slanted wells.
Another type of centralizer is a bow spring centralizer. Bow spring centralizers are often used instead of solid body centralizers because bow spring centralizers provide characteristics not possible with solid body centralizers. Bow spring centralizers have flexible bow spring arms that provide a spring force extending radially outwardly from the centralizer body. The bow springs are sufficiently flexible to facilitate travel of the centralizer through the well to the selected downhole elevation. To navigate constrictions in wells without binding the tool string, certain bow springs leave one spring end unattached to provide for compression of the bow spring through the constriction. The radial spring force provided by such bow springs is inherently limited by the need to provide for such flexural movement during installation.
Other spring configurations such as coiled springs have been used to urge centralizer arms against pipe casing. U.S. Pat. No. 3,978,924 to Roesner (1976) discloses a borehole instrument having pad assemblies attached to bow springs. U.S. Pat. No. 4,425,966 to Gamey (1984) discloses a tool having centralizing contact arms lockable in non-rotational positions to prevent translation along the tool shaft. U.S. Pat. No. 4,830,105 to Petermann (1989) discloses a centralizer having a tension coil spring for providing radial biasing forces. U.S. Pat. No. 5,358,040 to Kinley et al. (1994) discloses a mechanical arm centralizer for movement through restricted well pipe. U.S. Pat. No. 5,785,125 to Royer (1998) discloses arm support sleeves outwardly biased with springs.
Other techniques have also been developed to vary the holding forces provided by centralizers. U.S. Pat. No. 4,787,458 to Langer (1988) discloses a system for increasing the restoring force exerted by a bow spring against a casing or borehole wall. Protrusions on each bow spring increase the spring force while permitting sufficient flexure through wellbore constrictions. U.S. Pat. No. 5,934,378 to Tchakarov (1999) discloses a downhole drilling tool having upper and lower fingers operated by upper and lower actuators for engaging the fingers with the borehole wall.
The need for centralizers is particularly important in horizontal wellbores where the weight of tools and tubulars must be supported above the lower borehole wall. Special systems such as that disclosed in U.S. Pat. No. 5,992,525 to Williamson et al. (1999) have been developed to facilitate tool string deployment in horizontal and slanted wells.
Various systems have also been developed to deactivate centralizers. U.S. Pat. No. 5,566,754 to Stokka (1996) discloses a centralizer having rigid members collapsible under a lateral load of twenty tons. Tubular fluid pressure has also been used to deactivate centralizers as disclosed in U.S. Pat. No. 5,758,723 to Saucier et al. (1998), wherein a centralizer having arms in the normally extended position is deactivated by movement of a fluid pressure activated piston.
U.S. Pat. No. 5,575,333 to Lirette et al. (1996) discloses another type of spring bow unloading system wherein one end of each spring bow is attached to a centralizer body and the other end of each spring bow is attached to a floating collar. Radial compression of the spring bows due to a wellbore constriction causes movement of the floating collar without increasing the restoring force provided by the spring bows.
Conventional centralizer designs do not, however, permit control over the expandability provided by the centralizer arms. Accordingly, a need exists for an improved centralizer capable of deployment through well constrictions while providing downhole expandability with controllable radial force capabilities.
The preferred embodiment provides a centralizer for use downhole in a well. The centralizer comprises a body movable into the well, a contact arm having a first end stationary relative to the body and having a second end, wherein the contact arm is movable in a direction radially outwardly from the body, and a collar engaged with the contact arm second end, wherein the collar is selectively movable relative to the body to move the contact arm radially outwardly from the body. The collar is preferably movable by selected pressurization of a fluid within the well but may be controlled by other sufficient means. A lock also retains the contact arm in selected orientations relative to the body to maintain the centralizer radial force as the collar moves. Alternatively, the centralizer may not include the lock at all.
In different embodiments of the invention, the collar can be movable axially relative to said body in a direction toward said contact arm first end, the collar can be movable by selected pressurization of a fluid within the well, and a lock can retain the contact arm in selected orientations relative to the body to maintain the centralizer holding force.